Apparatus for continuously rolling steel billets

ABSTRACT

A plurality of materials are rolled in an upstream stand. While transfer speed of a succeeding material and the front end position thereof are detected, the transfer speed and the rear end position of a preceding material are detected by a measuring roll. The transfer speed of the succeeding material is controlled by adjusting at least the drive speed of the pinch rolls so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder. the rear end of the preceding material is joined with the front end of the succeeding material by flash-butt welding using the travelling welder to form a continuous material while letting the travelling welder move at a speed synchronous with the transfer speed of the continuous material. The welded portion on the continuous material is ground and/or cut to remove burr therefrom. After removing the burr, the continuous material is continuously rolled by a down-stream stand, and apparatus for carrying out the above-described method.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a method for continuous rolling by continuously welding the rolled materials at intermediate stage of a rolling line after applying several passes of rolling of billets, and relates to an apparatus therefor.

[0003] 2. Description of the Related Art

[0004] A known continuous rolling method to produce wire, rod, or shape steel with energy-saving and high efficiency comprises the steps of discharging billets from a heating furnace one at a time, welding the rear end of a preceding billet with the front end of a succeeding billet by a single unit of travelling flash-butt welder, removing the burr from the welded portions using a scarfer or the like, heating thus formed continuous billet to a temperature necessary for rolling in an induction heating furnace, then continuously-rolling the continuous billet in a rolling mill group: (disclosed in, for example, unexamined Japanese patent publication No.52-43754(1977)). Alternatively, there is a continues rolling method in which billets discharged from a heating furnace are joined together by welding to form a continuous billet, and the continuous billet is heated again in the heating furnace, wherein also a single unit of travelling flash-butt welder is used: (disclosed in, for example, examined Japanese patent publication No.52-11722(1982)

[0005] Shortening the cycle time for treating a single billet is an important issue in the continuous rolling of billets. In this respect, the weight of an ordinary billet is in a range of from 0.5 to 2 ton, and necessary cycle time to treat a single billet is within 1 min. to assure the production capacity of 70 to 80 ton/hr or more. Since conventional continues rolling processes use only one on-line travelling flash-butt welder, as described above, the welding time inherent to the travelling flash-butt welder is difficult to shorten. Consequently, it is impossible to actualize the cycle time of less than 1 min. in the prior art.

[0006] An applicable measures is to locate two units of travelling welder to realize a short cycle time operation. However, a system of two travelling welders increases investment cost and requires large capacity of power source. Further-more an applicable measures is to reduce the cross sectional area of billet through rolling in a specific number of rolling mill groups, to left the intermediate rolled materials in a free state, to adjust the position of the intermediate rolled materials, and to perform the weld-joining to reduce the welding time. The measures, however, has a disadvantage that, when the intermediate rolled materials become long, the measures cannot be adopted owing to the limitation of interstand distance.

SUMMARY OF THE INVENTION

[0007] An object of the present invention is to provide a method of continuous rolling which shortens the cycle time of billet treatment without requesting a large-scale modification of existing facilities, and provide an apparatus therefor.

[0008] The first method for continous rolling comprising the steps of: successively rolling a plurality of materials by a first rolling mill group; pinching a succeeding material after rolled in the first rolling mill group by a set of pinch rolls, detecting the transfer speed of the succeeding material and the position of a front end thereof, and detecting the transfer speed of a preceding material and the position of a rear end thereof; controlling the transfer speed of the succeeding material by adjusting the rotational speed of the pinch rolls so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder; after the front end of the succeeding material contacted with the rear end of the preceding material, joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding using the travelling welder to form a continuous material while letting the travelling welder move at a speed synchronous with the transfer speed of the continuous material; removing burr from a welded section on the continuous material; and continuously rolling the continuous material, after removing the burr, by a second rolling mill group located at downstream side from the burr-removing step.

[0009] The first apparatus of continuous rolling comprising: a first rolling mill group for successively rolling a plurality of materials; a travelling welder for joining a rear end of a preceding material with a front end of a succeeding material by flash-butt welding to form a continuos material while moving itself at a speed synchronous with the transfer speed of the materials; a travelling burr-removing machine for removing burr from a welded portion of the continuous material;

[0010] a second rolling mill group located at down-stream side of the travelling burr-removing machine for continuously rolling the continuous material after removing the burr; wherein the travelling welder, the travelling burr-removing machine, and the second rolling mill group are in linear arrangement.

[0011] The second method for continuous rolling comprising the steps of: successively rolling a plurality of materials by a first rolling mill group; pinching a succeeding material after rolled in the first rolling mill group by a set of pinch rolls, controlling the transfer speed of the succeeding material and the position of a front end thereof, and detecting the transfer speed of a preceding material and the position of a rear end thereof; controlling the transfer speed of the succeeding material by adjusting the rotational speed of the pinch rolls so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder; after the front end of the succeeding material contacted with the rear end of the preceding material, joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding using the travelling welder to form a continuous material while letting the travelling welder move at a speed synchronous with the transfer speed of the continuous material; grinding a welded section on the continuous material to remove burr therefrom; and continuously rolling the continuous material, after removing the burr, by a second rolling mill group located at downstream side from the burr-removing step.

[0012] The second apparatus for continuous rolling comprising: a first rolling mill group for successively rolling a plurality of materials; a set of pinch rolls for pinching a succeeding material after rolled and for detecting the transfer speed of the pinched material; a front end detector located at inlet of the pinch rolls for detecting a front end of the succeeding material; a measuring roll for detecting the transfer speed of a preceding material which is transferred before the succeeding material; a rear end detector located at inlet of the measuring roll for detecting a rear end of the preceding material; a travelling welder located at down-stream side of the measuring roll for joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding to form a continuous material while moving itself at a speed synchronous with the transfer speed of the continuous material; a travelling burr-removing machine for removing burr from a welded portion of the continuous material; a secondary rolling mill group located at down-stream side of the travelling burr-removing machine for continuously rolling the continuous material after removing the burr; and a drive control unit to which signals from the pinch rolls, the front end detector, the measuring roll, and the rear end detector are entered, and in which the rotational speed of the pinch rolls or both the rotational speed of the pinch roll and the rolling speed of the first rolling mill-group are determined so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder, and these determined variables are controlled; wherein the pinch rolls, the measuring roll, the travelling welder, the travelling burr-removing machine, and the second rolling mill group are in linear arrangement.

BRIEF DESCRIPTION OF THE DRAWING

[0013]FIG. 1 illustrates a construction of the continous rolling apparatus in the first mode according to the present invention.

[0014]FIG. 2 is a time chart indicating an example of motion of continous rolling apparatus in the first mode according to the present invention.

[0015]FIG. 3 illustrates a construction of the continous rolling apparatus in the second mode according to the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

[0016] 1. The First Mode:

[0017]FIG. 1 illustrates the arrangement of apparatus for continuous rolling of a mode according to the present invention. The figure shows a fourth stand 10 and a fifth stand 11 in the rolling mill group. The first stand (not shown) through the fourth stand 10 are assumed to structure the roughing mill group, and the fifth stand 11 and succeeding stands are assumed to structure the intermediate rolling stands. Between the fourth stand 10 and the fifth stand 11, there arranged a travelling hot saw 21, a descaler 22, a table 23, a travelling flash-butt welder 24 (hereinafter referred to simply as the “travelling welder”), a travelling burr-removing machine 25, and an induction heating unit 26, in series.

[0018] The following is the description of the functioning state of the apparatus of FIG. 1. A material 50 left from the fourth stand 10 enters the travelling hot saw 21 where the front end thereof is crop-cut. The crop-cutting is done to obtain a suitable shape (or existence of no significant collapse at edge) for succeeding flash-butt welding (FBW). Even when a travelling cutting machine is applied instead of the hot saw, the cutting machine shall minimize the collapse of material. The material 50 after passed the fourth stand 10 becomes free. Then the material 50 is sent by the table 23 so as the material 50 to catches up with the rear end of the preceding material when the rear end arrives at the center of home position of the travelling welder machine 24. The descaler 22 located at inlet of the travelling welder 24 removes scale at the clamped portions on front end and rear end of the transferred materials. The travelling burr-removing machine 25 is located after the moving end of the travelling welder 24. The travelling burr-removing machine 25 conducts burr-removal at the welded portion of the materials welded by the travelling welder 24 while moving thereof. The materials welded by the travelling welder 24 are cooled at their clamped portions during welding. The induction heating unit 26 located at inlet of the fifth stand 11 heats the cooled portions, then the unit 26 sends the materials to the fifth stand 11.

[0019] The cut of the material at its rear end is conducted at a point that the rear end passes through the home position of the travelling hot saw 21. At that moment, if the material is in completely free state (or in a state that the material passed through the fourth stand and that the material is not clamped by the travelling welder 24), then the cutting in a stopped state is also possible.

[0020]FIG. 2 is a time chart illustrating an example of motion of continuous rolling apparatus of FIG. 1. For example, the material {circle over (2)} discharged from the fourth stand 10 is crop-cut at its front end by the travelling hot saw 21. At that moment, the material {circle over (2)} is still caught by the fourth stand 10, so the travelling hot saw 21 conducts the cutting action while moving at a speed synchronous with the transfer speed of the rolled material. When the material {circle over (1)} passed through the fourth stand 10, the table 23 feeds the material {circle over (2)} so as the front end thereof to catch up with the rear end of the preceding material {circle over (1)} at a point that the rear end of the preceding material {circle over (1)} arrives at the center of the waiting position in the travelling welder 24. During the feeding period, the rear end of the material {circle over (2)} passes through the travelling hot saw 21 so that the rear end of the material {circle over (2)} is cut. The cutting of rear end of the material {circle over (2)} may be conducted while moving thereof. Since, however, during the moving period, the material {circle over (2)} is in free state, the cutting may be done by stopping the movement of the material and may be done in a stopped state, if only the cycle time allows.

[0021] The travelling welder 24 begins to move at a point that the front end of the succeeding material {circle over (2)} catches up with the rear end of the preceding material {circle over (1)}, and conducts flash-butt welding (FBW) after clamping the materials {circle over (1)} and {circle over (2)}. According to the chart of FIG. 2, the rolling cycle of billet is selected to 40 sec. including 20 sec. for welding and 18 sec. for returning. Since the material treated in this step is an intermediate material, the cross sectional area of the material is narrower than that of billet (about one fourth after the fourth stand), and welding in a short time is available. After completing the welding step, the travelling burr-removing machine 25 conducts burr-removal in moving state. FIG. 2 shows a burr-removal cycle of 12 sec. including 6 sec. for burr-removal and 6 sec. for returning. The induction heating unit 26 located at inlet of the fifth stand 11 conducts heating and soaking of the materials. Since, however, the time for the material from leaving the fourth stand 11 to entering the fifth stand is 120 sec. or less, and since there occurs not significant temperature reduction, rather heating and soaking of the locally cooled portion at clamped portions are important. In this respect, it is effective that the induction heating unit 26 is also a travelling type, if space allows.

[0022] 2. The Second Mode:

[0023]FIG. 3 illustrates the arrangement of apparatus of continuous rolling of a mode according to the present invention. The figure shows an upstream stand 10 and a down-stream stand 11 in the rolling mill group. The first stand (not shown) through the upstream stand 10 are assumed to structure the rough roll group. A travelling cutting machine 21 is located at upstream side of exit of the upstream stand 10. A set of pinch rolls 27 which is controllable in the driving speed thereof is located at downstream side of the travelling cutting machine 21. A measuring roll 28, a descaler 22, a travelling flash-butt welder 24 (hereinafter referred to simply as “travelling welder”), and a travelling burr-removing machine 25 are arranged in series at down-stream side of the pinch rolls 27. A travelling induction heating unit 26 is located at inlet of the down-stream stand 11. Since the mode has a short distance between stands, and temparature reduction of the material occurs very little, no stationary induction heating unit for heating total material is applied.

[0024] At the inlet of each of the taravelling cutting machine 21, the pinch rolls 27, and the measuring roll 28, a respective material detector 30, 31, and 32, is positioned. The detector 30 detects the front end and the rear end of material, and the detection signal generated from the detector 30 is used for controlling the movement of the travelling cutting machine 21. The detector 31 detects the front end of material, and the detector 32 detects the rear end of material. The drive control unit 40 receives the detection signals generated from the detector 32, the rotary encoder 42 attached to the drive motor 41 which drives the pinch rolls 27, and the rotary encoder 43 attached to the measuring roll 28, and controls the drive motor 44 of the upstream stand 10 and the drive motor of the pinch rolls 27 based on the received detection signals. The drive control unit 45 receives the detection signal generated from the detector 30 to control the travelling cutting machine 21.

[0025] The following is the description of the functioning state of the apparatus of FIG. 3. A material rolled in the upper stand 10 arrives at the detector 30 where the arrival of front end of the material is detected. The drive control unit 45 drives the travelling cutting machine 21 based on the detection signal to conduct crop-cutting of the front end of the material. When the detector 30 detects the rear end of a material, the travelling cutting machine 21 is controlled for its movement in a similar manner to conduct crop-cutting of the rear end of the material. The cutting is done to obtain a suitable shape (or existence of no significant collapse at edge) for succeeding flash-butt welding (FBW). Accordingly, the travelling cutting machine 21 is requested to be the one that generates very little collapse at cutting edge. A travelling saw may be applied as the travelling cutting machine 21. The material which was crop-cut at its end in the travelling cutting machine 21 then arrives at the detector 31 where the arrival of front end thereof is detected. On arrival of the front end of the material at the detector 31, the material is pinched by the pinch rolls 27 at slightly rear side from the front end thereof. The speed of the material at that moment at the exit of upstream stand 10 is set to a slightly higher value than the inlet speed of the continuous material to the down-stream stand 11 (determined by the rotary encoder 43 in the measuring roll 28), and the pinch rolls 27 are also driven synchronously with the speed of the material.

[0026] After the succeeding material is pinched by the pinch rolls 27, the transfer speed and the front position of the succeeding material are detected by the pinch rolls 27. That is, the transfer speed of the material is detected by the rotary encoder 42, and the front end of the material is detected by the detector 31, thus tracks the movement of the material using a drive control unit 40 to detect the transfer speed and the front end position of the succeeding material. As for the preceding material, the transfer speed is detected by the rotary encoder 43 in the measuring roll 28, and the rear end position is detected by the detector 32, thus tracking the movement of the preceding material using the drive control unit 40 to detect the transfer speed and the front end position of the succeeding material. The drive control unit 40 computes the transfer speed of upstream material so as the front end of the succeeding material and the rear end of the preceding material to contact each other at a target position before the travelling welder 24 based on the relative relation between the transfer speed and front end position of succeeding material and the transfer speed and rear end position of preceding material, then controls the rotational speed of the drive motor 44 of the upstream stand 10 and the drive motor 41 of the pinch rolls 27.

[0027] Through the control described above, the rear end of preceding material and the front end of succeeding material contact with each other at a target position. The drive control unit 40 detects the contact of materials from the increased torque (increased drive current) on the pinch rolls 27 or from the thrust force applied to the pinch rolls 27 toward upstream side, and controls the transfer speed (rolling speed) at upstream side to synchronize with the rolling speed at down-stream side. At a moment that the succeeding material and the preceding material arrive at the home position of the travelling welder 24 in a state of adjoining and synchronously running thereof, the travelling welder 24 begins the welding of these materials while moving by itself synchronously with the transfer speed of the materials. The descaler 22 which is located at inlet of the travelling welder 24 performs descaling at the clamped portion at both front end and rear end of the transferred material. After the travelling welder 24, there positioned the travelling burr-removing machine 25 which conducts burr-removal at the portion welded by the travelling welder 24 in a moving mode. The material welded by the travelling welder 24 is cooled at its clamped portion during welding. The induction heating unit 26 located at inlet of the downstream stand 11, however, heats the locally cooled portion before transferring the material to the down-stream stand 11.

[0028] According to the above-described welding process, the transfer speed of the succeeding material is controlled against the transfer speed of the preceding material responding to respective welding condition for flash-butt welding and for upset-welding. The control is performed through the control of upset cylinder which is built in the travelling welder 24. The speed control of the upstream (succeeding) material corresponding to the control of the upset-cylinder differs with variables such as billet size, intermediate material size, and distance between the welder and the upstream stand.

[0029] 1) In the case that the rear end of the succeeding material passes through the upstream stand 10 and that the succeeding material becomes free before the welding begins, (or that the succeeding material passed through the upstream stand 10 and the succeeding material is not clamped by the travelling welder 24), the welder clamps the succeeding material, then the pinch rolls 27 release the material. That is, the case occurs for a short intermediate material passed through the upstream stand 10. The case is controlled in a similar procedure as prior art.

[0030] 2) In the case that the cross sectional area of intermediate material is relatively narrow and the length thereof is long, (50 sq. to 100 sq.), the speed variation is absorbed by a material loop height between the upstream stand 10 and the pinch rolls 27. Since the speed variation in that case is slight, the necessary height of material loop is very small (100 to 200 mm), the material loop height is easily formed if only the distance between the upstream stand 10 and the pinch rolls 27 is secured.

[0031] 3) In the case that the cross sectional area of the intermediate material is wide and that the length thereof is large, the formation of material loop height is difficult so that the speed control is applied by an integral motion of the upstream stand 10 and of the pinch rolls 27. since the change cycle of transfer speed of the material is at a level of several Hz, conventional tension control is applicable.

[0032] As described above, according to the present invention, materials that were reduced in their cross sectional area by rolling in the first rolling mill group are joined together by flash-butt welding in a travelling welder to form a continuous material, and the burr on the welded portions of the continuous material is removed, followed by continuous rolling of the continuous material in a second rolling mill grfoup. Accordingly, shortening of billet treatment cycle time is realized without requesting significant modification of existing facilities, and a succeeding material rolled in and discharged from the first rolling mill group is pinched by a set of pinch rolls, and the transfer speed and the front end position of the succeeding material are detected, also the transfer speed and the rear end position of the preceding material are detected. Then the transfer speed of the succeeding material is controlled so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder through the adjustment of the drive speed of the pinch rolls or both the drive speed of the pinch rolls and the first rolling mill group. Thus the materials which were reduced in the cross sectional area thereof by rolling are successively welded together by the travelling welder to form a continuous material. As a result, the welding time is shortened, the continuous welding of billets is performed independent of billet size and intermediate material length, and the cycle time for treating billets is shortened. Since the method according to the present invention is not limited by billet size, the method is applicable to a rolling mill group having relatively short distance between both stands. 

What is claimed is:
 1. A method for continuous rolling comprising the steps of: successively rolling a plurality of materials by a first rolling mill group; joining a rear end of a preceding rolled material with a front end of a succeeding rolled material by flash-butt welding to form a continuous material using a travelling welding machine while moving thereof at a speed synchronous with the transfer speed of the materials; removing burr from a welded portion on the continuous material; and continously rolling the continous material, after removing the burr, by a second rolling mill group located at down-stream side from the burr-removing step.
 2. An apparatus of continuous rolling comprising: a first rolling mill group for successively rolling a plurality of materials; a travelling welder for joining a rear end of a preceding material with a front end of a succeeding material by flash-butt welding to form a continuos material while moving itself at a speed synchronous with the transfer speed of the materials; a travelling burr-removing machine for removing burr from a welded portion of the continuous material; and a second rolling mill group located at down-stream side of the travelling burr-removing machine for continuously rolling the continuous material after removing the burr, wherein the travelling welder, the travelling burr-removing machine, and the second rolling mill group are in linear arrangement.
 3. An apparatus of claim 2 , wherein the first rolling mill group comprises a rough-stand group.
 4. An apparatus of claim 2 further comprises an induction heating unit located at inlet of the second rolling group.
 5. An apparatus of claim 3 further comprises an induction heating unit located at inlet of the second rolling group.
 6. A method for continuous rolling comprising the steps of: successively rolling a plurality of materials by a first rolling mill group; pinching a succeeding material after rolled in the first rolling mill group by a set of pinch rolls, detecting the transfer speed of the succeeding material and the position of a front end thereof, and detecting the transfer speed of a preceding material and the position of a rear end thereof; controlling the transfer speed of the succeeding material by adjusting the rotational speed of the pinch rolls so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder; joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding using the travelling welder to form a continuous material, after the front end of the succeeding material contacted with the rear end of the preceding material, while letting the travelling welder move at a speed synchronous with the transfer speed of the continuous material; removing burr from a welded portion on the continuous material; and continuously rolling the continuous material, after removing the burr, by a second rolling mill group located at downstream side from the burr-removing step.
 7. An apparatus for continuous rolling comprising: a first rolling mill group for successively rolling a plurality of materials; a set of pinch rolls for pinching a succeeding material after rolled and for detecting the transfer speed of the pinched material; a front end detector located at inlet of the pinch rolls for detecting a front end of the succeeding material; a measuring roll for detecting the transfer speed of a preceding material which is transferred before the succeeding material; a rear end detector located at inlet of the measuring roll for detecting a rear end of the preceding material; a travelling welder located at down-stream side of the measuring roll for joining the rear end of the preceding material with the front end of the succeeding material by flash-butt welding to form a continuous material while moving itself at a speed synchronous with the transfer speed of the continuous material; a travelling burr-removing machine for removing burr from a welded portion of the continuous material; a secondary rolling mill group located at down-stream side of the travelling burr-removing machine for continuously rolling the continuous material after removing the burr; and a drive control unit to which signals from the pinch rolls, the front end detector, the measuring roll, and the rear end detector are entered, and in which the rotational speed of the pinch rolls or both the rotational speed of the pinch roll and the rolling speed of the first rolling mill group are determined so as the front end of the succeeding material to contact with the rear end of the preceding material at a specified position in a travelling welder, and these determined variables are controlled, wherein the pinch rolls, the measuring roll, the travelling welder, the travelling burr-removing machine, and the second rolling mill group are in linear arrangement.
 8. An apparatus of claim 7 further comprising: a front/rear end detector located at exit of the first rolling mill group for detecting the front end and the rear end of materials discharged from the first rolling mill group; and a means located in between the front/rear end detector and the pinch rolls for crop-cutting the front end of the succeeding material and the rear end of the preceding material while moving by itself.
 9. An apparatus of claim 7 further comprising: a travelling induction heating unit located at inlet of the second rolling mill group.
 10. An apparatus of claim 8 further comprising: a travelling induction heating unit located at inlet of the second rolling mill group. 